Evidence of artemisinin partial resistance in Zambia: a molecular epidemiology and clinical study.
Abstract
Background
Artemisinin derivatives are central to first-line treatment of both uncomplicated and severe Plasmodium falciparum malaria. Emerging artemisinin partial resistance in east Africa threatens to spread across the continent.
Methods
In two cross-sectional studies conducted across the ten provinces of Zambia in 2024, we genotyped the artemisinin resistance-associated gene Pfkelch13. Children aged 6-72 months were recruited from randomly selected households in the first study, and patients 6 months or older presenting with malarial symptoms at 100 selected health facilities were recruited in the second study. In Kaoma, western Zambia, we recruited patients aged 12 months or older with microscopically confirmed P falciparum infection and a positive rapid diagnostic test. We evaluated the association between Pfkelch13 genotype and day 3 parasite positivity following treatment with artemisinin-based combination therapy, as well as ex-vivo parasite susceptibility to dihydroartemisinin (the active metabolite of artemisinin). We also assessed longitudinal changes in Pfkelch13 mutation prevalence in Kaoma using isolates collected during therapeutic efficacy studies and community surveys conducted from 2018 to 2026.
Findings
We identified a novel mutation, Pfkelch13 A724E, in 113 (52%) of 217 isolates (95% CI 45-59) from Western Province, 94 (51%) of 184 isolates (95% CI 44-59) from North-Western Province, and 229 (11·7%) of 1949 isolates countrywide. In Kaoma, 28% (21 of 75 [95% CI 18-40]) of patients carrying Pfkelch13 A724E mutant parasites before treatment were parasite-positive on day 3, compared with 0% (zero of 23; [0-15]) of patients with the wild-type allele (p=0·0026). Within the patients who were positive at day 3, the proportion of A724E mutant parasites increased significantly after treatment (p=0·0039). The prevalence of Pfkelch13 A724E in Kaoma increased steadily from 0% (0 of 15 isolates [95% CI 0-22]) in 2018 to 79% (132 of 167 [73-85]) in 2026. No significant ex-vivo growth inhibition was observed in Pfkelch13 A724E parasites after dihydroartemisinin exposure.
Interpretation
A novel Pfkelch13 mutation clinically associated with partial resistance to artemisinin is spreading in Zambia. Additional clinical evaluations are urgently needed in the region.
Funding
The Gates Foundation (INV-048316).